1. Field of the Invention
The present invention relates to control systems for air conditioners that utilize a compressor to compress coolant to cool a recycling heat transfer fluid, where the heat transfer fluid in turn is used to cool ambient air.
2. Description of the Prior Art
Most commercial building air conditioning systems employ one or more centrifugal compressors which compress a coolant, such as freon. The coolant is passed through a line into thermal contact with a recycling heat transfer fluid, such as water. The coolant is allowed to expand thereby cooling the water. The water is cycled through a radiator system, past which air to be cooled is blown. The water cools the air and then returns to thermal contact with the air conditioner coolant to give up the heat absorbed from the air. Cooling of the ambient air thus proceeds in recycling fashion. Because of the use of water as an intermediate recycling heat transfer fluid, such air conditioning systems are referred to as chilled water air conditioners, or chiller air conditioning systems.
Control of the amount of heat removed from ambient air in a chiller air conditioning system is effectuated by regulating the amount of coolant supplied to the centrifugal compressor. Coolant is usually forced through a system of vanes, which can be opened or closed to an adjustable degree depending upon the amount of coolant to be supplied to the compressor. As the vanes are opened, a greater amount of coolant is supplied to the compressor, and hence cooling capacity is increased. Closing the vanes limits the amount of coolant supplied to the compressor, and thereby reduces the degree to which the air conditioning system cools the ambient air.
When commercial chiller air conditioning systems are initially turned on, they initially place a huge power demand on the commercial electrical utility which supplies power for operation. In a typical system that normally draws approximately 125 amps once it has reached normal running conditions, there is an initial 280 amp surge as measured over the initial 15 minute interval that the system is turned on. This initial power surge represents a unnecessary power drain and inordinately increases electrical power consumption by the air conditioning system. Moreover, public utilities must construct and maintain adequate facilities to service such peak power loads, even though these loads fall off sharply after the initial start-up period. As a result, public utilties are forced to construct power plants adequate to service such large initial loading. Furthermore, because of the high initial loading, customers utilizing conventional chiller air conditioning systems are billed for electrical service at a rate reflecting the high electrical load demand that the initial supply of power to the systems requires, rather than the lower average power demand of the air conditioning system.
A further characteristic of conventional commercial chiller air conditioning systems is that they are controlled in response to the temperature of the chilled water as it leaves thermal contact with the coolant. As a result, there is a considerable amount of overshooting and undershooting of actual room temperature. This leads to an inordinately high average power demand by the air conditioning system. Furthermore, in conventional chiller air conditioning systems the vanes admitting the supply of coolant to the compressor are adjusted in the same fashion regardless of whether the supply of coolant is being increased or decreased. This likewise leads to an inordinately high average power demand by the air conditioning system.